Control member with tensed cables

ABSTRACT

The control unit includes an arm ( 21 ) sliding inside of a sheath ( 20 ) the angle of which can be varied and which is supported by three tensed cables ( 25; 26; 27 ) arranged in a triangle and unwinding with a certain degree of resistance from force feedback motors ( 16; 17; 18 ). The wrist ( 23 ) of the control unit can be moved according to at least the three degrees of translational freedom, without having to be afraid of encountering the cables; the control unit is simple, inexpensive and possesses a satisfactory degree of stiffness. A friction-creating means, possibly consisting of another tensed cable and dependant on a motor, is placed between the sheath ( 20 ) and the arm ( 21 ). 
     This unit can be used for telemanipulation, telesurgery, CAD, games, etc.

The subject of this invention is a control unit one essential element ofwhich is a set of tensed cables.

The known control units or master arms used in various fields rely ondifferent mechanisms. Arms consisting of successive articulated sectionshave thus been proposed, which, however, possess a certain degree ofcomplexity, a significant degree of inertia, and kinematic singularitiesthat limit the movements that can be imposed on them. This is why othertypes of units have again been proposed.

Thus, a known control unit includes a thimble-shaped operating deviceinto which the user inserts a distal phalanx, and that is suspended fromfour tensed cables which, in the embodiment proposed by the authors, areunwound from the vertices of a regular tetrahedron, or else over four ofthe vertices of a cube, always diametrically opposite each other on thefaces of the cube. The force feedback motors, which ensure tensioning ofthe cables, are arranged at these vertices. By moving the thimble, theuser varies the unwound lengths of the cables, and the correspondingmeasurements make it possible to perform the desired control. Thismechanism is simple and easy to use, but has the disadvantage of beingcumbersome, the cables running in every direction from the thimble.

The invention proposes a novel control unit arrangement whose structureis simple and inexpensive and that can be easily endowed with asufficient degree of stiffness. In its more general shape, the controlunit of the type with tensed cables, arranged between a generallystationary base and a movable wrist and equipped with an element graspedby the operator, is characterized in that it includes: a sheath joinedto the base by a double joint; three actuating cables between the sheathand the base and connecting to the base at the same number of connectingpoints surrounding the sheath; an arm supporting the wrist, sliding intothe sheath; and an actuating means between the arm and the sheath.Within the meaning of the invention, the cables and actuating meansensure the active control of the movements of the unit, i.e., that theirfree length, or more generally their condition, is variable, but thatthey maintain the unit in a fixed position at rest and exert a certainresistance to the movements of the unit imposed by the user, in order togive the unit a degree of stiffness that enables a more pleasant andaccurate control. The conventional means in this technology consist of aso-called force feedback motor, most often equipped with an encoder thatmeasures its movements and transmits them to the machine controlled bythe unit, in order to thus also contribute to the control.

The invention will now be described in detail by means of the followingfigures:

FIG. 1 shows the previously described known control unit with cable;

the four FIGS. 2, 3, 4, and 5 show as many embodiments of the invention,and FIGS. 2A and 2B are two sections through the unit in the embodimentof FIG. 2, according to two alternative embodiments.

FIG. 1, therefore, shows four similar cables 1 to 4 unwinding fromrespective motors 5 to 8 placed at the corners of a regular tetrahedronand all positioned on a stationary base not shown. The cables 1 to 4converge towards a thimble 9 into which an operator inserts his fingerand that he moves to the desired position by varying the unwound lengthsof the cables 1 to 4. A system such as this is described more fully inthe article “A 3D Spatial Interface Device Using Tensed Strings,” byIshii and Sato, published in the journal “Presence” (Volume 3, Number 1,Winter 1994, pages 81-86). The authors also mention that it is possibleto improve this system by splitting it into two within the same spaceand by installing another thimble whose cables would be unwound frommotors placed at the four unoccupied vertices of the cube and into whichthe operator would insert another finger of his hand, in particular thethumb.

The arrangement of the four motors is identical: in this way, the motor6 (the only one shown completely) includes an output shaft 10 thatrotates a pulley 11 inside of which the cable 3 is wound; the cable 3passes through a die 12 (at the vertex of the tetrahedron) that gives ita fixed point, and an angle encoder 13 is connected to the output shaft10 in order to follow its movements and communicate them to the machinecontrolled by the unit.

In the first embodiment of the invention of FIG. 2, the base of thecontrol unit bears the reference 15; it is planar and holds threeactuating motors 16, 17, 18 analogous to the motors already encountered,as well as a double joint 19 connected to a sheath 20. An arm 21 slidesinto the sheath 20 and exits therefrom via an open end 22 thereof, whichis opposite the double joint 19. The free end of the arm 20 supports awrist 23, i.e., a double or triple joint that makes it possible to tiltan element held by the operator, such as a pen 24 in any direction, andto possibly rotate it. Associated with the motors 16, 17 and 18 arecables 25, 26 and 27 that are stretched from a connection point at thebase 15, capable of being formed by a known die, such as 12, to the openend 22 of the sheath 20, whereon they are hooked while forming a networkof pyramid edges. A fourth cable 28 exists, housed inside the sheath 20and running along the arm 21, onto which it is hooked by its ends.However, it forms a loop at a location where it is wound around a pulleyof a fourth motor 29 fastened to the sheath 20, on its exterior face,while passing through a slot 30 of the sheath 20 perforated at thislocation. It is seen that the fourth cable 28, stretched between thesheath 20 and the arm 21, and its motor 29 together form an actuatingmeans between the sheath 20 and the arm 21. Skids 31 or any othersuitable means, visible in FIG. 2B, are arranged between the sheath 20and the arm 21 to enable a guided sliding movement.

The system consisting of the cables of the sheath 20 and the arm 21 is acontrol unit with three degrees of freedom, i.e., it makes it possibleto place the wrist 23 at any point of a workspace. The motors 16 to 18and 29 and the cables 25 to 28 make it possible to maintain the controlunit at the position that it reached while at the same time imposing astiffness satisfactory to the user during movements. The first threecables 25, 26, and 27 maintain the sheath 20 and the arm 21 on the base15, at the angle that was given to them according to the two firstdegrees of freedom of the unit, and the fourth cable 28 maintains thedegree of insertion given to the arm 21 inside the sheath 20 accordingto the third degree of freedom of the unit. As already mentioned, thewrist 23 may also be equipped with force feedback motors that make itpossible to control additional degrees of freedom related to the angleof the pen 24. It may also become useful to permit rotation of the arm21. The sheath 20 might then rotate together with the arm 21 byreplacing the double Cardan joint 19, which only makes it possible toadjust the angle of the sheath 20 on the base 15, with a triple balljoint. In order to prevent rotating movements of the arm 21 inside thesheath 20, and damage to the cable 28, it is anticipated to give themthe polygonal sections illustrated in FIG. 2B.

On the other hand, FIG. 2A shows an alternative embodiment where thesheath 20 and an arm 21 have circular concentric sections in order toenable the arm to rotate; if, depending on this rotation, a forcefeedback is desired, the fourth cable 28, at one end at least, may bewound around the arm 21, ahead of the skids 31. It comprises at leastone turn 28′ at this location. In this way, one degree of freedom hasbeen added. Translational and rotational force feedback movements canalso be obtained by using an additional motor.

In this embodiment, the space intended for the user is very open sinceall of the cables run beneath it; but the control stiffness remainssomewhat poor, which justifies the somewhat different arrangement ofFIG. 3. In this case, the double joint 19 (or the ball joint) and thepoints for hooking up the first three cables 25, 26 and 27 to the sheath20 have been transposed, i.e., the double joint 19 is now near the openend 22 of the sheath, hooked onto a gallows-like support 32 of the base15, and the lower end 33 of the sheath 20 supports a hook-up point 34for the cables 25, 26 and 27, which are now substantially coplanar. Itis immediately apparent that the stresses exerted by the user on thewrist 23 produces a smaller moment since the lever arm is reduced to thefree length of the arm 21, and the resistance of the motors 16 to 18 ismore difficult to overcome. Furthermore, the angle of the sheath 20 andof the cables 25 to 27 is generally greater than in the previousembodiment, with the result being that their tension exerts a greatermoment. These two differences give a greater degree of stiffness to thecontrol unit. It shall also be noted that greater angular tiltingmovements might possibly be communicated to the wrist 23, and that theworkspace is more open due to the greater distance of separation betweenthe first three cables 25 to 27 and the wrist 23. It is also possible toplace the motors 16 to 18 above the end 33, which permits greaterrotational travel at the cost of larger overall dimensions.

In the embodiment of FIG. 4, the overall design of FIG. 3 has been takenup again, but the fourth motor 29 is no longer situated on the sheath 20but on the support 32, and only one end of the fourth cable 28 runs overthe arm 21 and is hooked on to it; the add-on piece 28″ of the cableextends over the support 32 up to the motor 29 from where it unwinds.Furthermore, one of the first three cables, e.g., 27, extends beyond thefastening device 33 and enters into the sheath 20, and its end is hookedon to the arm 21. Thus, upon extension of the arm 21, the stiffness isproduced by the motor 18 of this cable 27, and the insertion stiffnessof the arm 21 is produced by the motor 29 of the fourth cable 28. Asbefore, the motor 18, like the motors 16 and 17, also serves to react tothe angular movements of the sheath 20.

Another embodiment not shown uses a cable attached at both of its endsto the arm 21 as in FIGS. 2 and 3, with a motor set off-center on thesupport 32, as in FIG. 4.

FIG. 5 shows a composite unit consisting of a pair of control units ofthe invention (e.g., as in FIG. 4), the two arms 21 being substantiallyparallel and their wrists 23 being joined by a connecting rod 34 holdingthe pen 24. The control unit made in this way has five degrees offreedom, without having to use a wrist with a complicated structure, asfor the previous embodiments. It is to be noted that the two basic unitsmay be rather close together without producing any large risk ofsingularity.

Therefore, the control unit proposed here offers a particularly simplestructure. It can be applied to the primary traditional or developingfields of master arm control, such as telemanipulation, telesurgery,games, computer-assisted design, etc.

1. Control unit with tensed cables arranged between a base (15) and amovable wrist (23), wherein the control unit includes: a sheath (20)joined to the base by a double joint (19); three actuating cables (25,26, 27) between the sheath and the base and connecting to the base atthe same number of connecting points surrounding the sheath; an arm (21)supporting the wrist (23), sliding into the sheath; and an actuatingmeans (28, 29) between the arm and the sheath.
 2. Control unit asclaimed in claim 1, characterized in that the actuating means includes acable (28) stretched between the sheath (20) and the arm (21) andcontrolled by a motor (29), and in that the three cables stretchedbetween the sheath (20) and the base (15) are controlled by respectivemotors (16, 17, 18).
 3. Control unit as claimed in claim 1,characterized in that the actuating means includes a cable (28)stretched between the arm (21) and the base (32) and controlled by amotor placed on the base, in that the three cables stretched between thesheath and the base are controlled by respective motors, and one of thethree cables extends beyond the sheath to a fastening point on the arm.4. Control unit as claimed in claim 1, characterized in that the threecables (25, 26, 27) are arranged like the edges of a pyramid, and thedouble joint (19) is surrounded by the connecting points of the cablesto the base.
 5. Control unit as claimed in claim 1, characterized inthat the three cables are substantially coplanar and the double joint(19) is placed at a location of the sheath (20) from which the arm (21)exits.
 6. Control unit as claimed in claim 1, characterized in that thedouble joint is a ball joint.
 7. Control unit as claimed in claim 1,characterized in that the arm is capable of being rotated inside thesheath.
 8. Composite control unit, characterized in that it includes apair of units according to any of the preceding claims, the base beingcommon to the units, the arms being joined to a common wrist by balljoints.
 9. Control unit as claimed in claim 1, wherein the cables extendoutside and around the sheath, at non-zero angles with the sheath. 10.Control unit as claimed in claim 1, wherein the double joint is a Cardanjoint.
 11. Control unit with tensed cables arranged between a base and amovable wrist including: a sheath joined to the base by a doublearticulation joint; first, second, and third actuating cables providedbetween the sheath and the base, wherein the first, second, and thirdcables are hooked to the sheath at a first end thereof and deliveredfrom first, second, and third motors at an opposite end thereof, whereinthe first, second, and third motors are connected to the base at a samenumber of connecting points surrounding the sheath; an arm supportingthe wrist, wherein the arm is slidable into the sheath, the first,second, and third cables having diverging directions from the sheath;and an actuating means between the arm and the sheath.
 12. Control unitof claim 11, wherein the actuating means includes a fourth cablestretched between the sheath and the arm and controlled by a fourthmotor, and wherein the first, second, and third cables stretched betweenthe sheath and the base are controlled by the respective first, second,and third motors.
 13. Control unit of claim 11, wherein the actuatingmeans includes a fourth cable stretched between the arm and the base andcontrolled by a motor placed on the base, and wherein one of the first,second, and third cables extends beyond the sheath to a fastening pointon the arm.
 14. Control unit of claim 11, wherein the first, second, andthird cables are arranged like edges of a pyramid, and the doublearticulation joint is surrounded by the connecting points of the first,second, and third cables to the base.
 15. Control unit of claim 11,wherein the first, second, and third cables are substantially coplanarand the double articulation joint is placed at a location of the sheathfrom which the arm exists.
 16. Control unit of claim 11, wherein thedouble articulation joint is a ball joint.
 17. Control unit of claim 11,wherein the arm is capable of being rotated inside the sheath.
 18. Acomposite control unit comprising a pair of units according to any ofthe preceding claims, the base being common to the units, the arms beingjoined to a common wrist by ball joints.
 19. Control unit as claimed inclaim 11, wherein the cables extend outside and around the sheath, atnon-zero angles with the sheath.
 20. Control unit as claimed in claim11, wherein the double joint is a Cardan joint.